My ColdFusion instance and Mailchimp stopped talking to each other, because MailChimp APIs were upgraded to no longer support earlier versions of TLS. I communicated with MailChimp APIs using cfhttp. I knew that most things were slowly moving to TLS 1.2 and recently upgraded IIS to force it to use the newer protocol. I did not realize that some older versions of ColdFusion server were not already using it.

This is a perfect explanation of the errors I was seeing when my site tried to integrate with Mailchimp APIs. A vague connection refused error.

Since a full CF Upgrade was not on the table at this time, our solution was to upgrade the underlying JVM to 1.8. And once we did that we just needed to add this parameter:

view plain print about

Into the JVM Arguments in the ColdFusion administrator. You could also tweak the jvm.config file in your `cfrootinstall/cfusion/bin` directory.

I wish MailChimp notified me of this change before it was done, especially if my systems were communicating with outdated protocols, but at least now the issue is clear.